So, you will pay a $35 (or less) co-pay in the plan's Initial Deductible, Initial Coverage Phase, and the Coverage Gap (or Donut Hole).
However, if you spend over your annual out-of-pocket threshold or TrOOP ($6,550 in 2021 or $7,050 in 2022) and enter Catastrophic Coverage (the fourth and final phase of Part D drug coverage), you will pay 5% of the retail cost (so you may pay slightly more or less than your previous $35 co-pay - depending on the insulin's retail drug cost).
The Good News: Most people never reach the Catastrophic Coverage phase of their Medicare Part D coverage.
Medicare.gov Plan Finder Example of Co-Pay changes in Catastrophic Coverage
As an example of how Senior Savings Model insulin coverage can change through the phases of your drug plan, you can see in this Medicare.gov Plan Finder illustration of the 2021 WellCare Wellness Rx plan how coverage for two different types of insulin is at a $35 co-pay in the Initial Deductible (the 2021 plan's $445 deductible is not applicable), in the Initial Coverage Phase, and in the plan's Coverage Gap (Donut Hole).
However, if you reach the plan's Catastrophic Coverage phase you can see that the Medicare.gov Plan Finder shows that you will pay 5% of retail drug prices for the insulin - and not the $35 co-pay.
So, following the example of these two different types of insulin covered by the WellCare Senior Savings Model, you can see that the monthly drug cost increases for one type of insulin (from $35 up to $47.83) and decreases for another type of insulin (from $35 down to $21.96).